Effect of triangular cross-sectional transverse wedge on the performance of an inline tube bundle heat exchanger

ABSTRACT

In order to have a heat transfer per volume, heat exchangers have to have high overall heat coefficient. The effects of a transverse wedge on the heat transfer, the pressure drop, and the thermal efficiency factor (TEF) of air flow through a tube bundle heat exchanger was investigated. TEF increases continuously with the wedge aspect ratio (α). Form α = 0.275, 0.550, 0.758 to 1, TEF increases continuously from 1.157 to 1.84, 1.11 to 1.72, 1.05 to 1.42, and 1.02 to 1.39 for x/L = 1/3, 2/3, 1, and 0, respectively.

KEYWORDS:

• Tube bundle
• Heat transfer enhancement
• Thermal efficiency factor
• Liquid to air heat exchanger
• Transverse wedge

Acknowledgments

The authors acknowledge Mr. Ian Thomas for making the manuscript more readable.

Disclosure statement

No potential conflict of interest was reported by the authors.

Nomenclatures

$A_c$	=	duct across sectional area [$m^2$]
$\sum A_o$	=	total outer surface area of the tube [$m^2$]
$b$	=	wedge base [$m$]
$e$	=	wedge height [$m$]
$D$	=	tube diameter [$m$]
$D_h$	=	hydraulic diameter of the heat exchanger [$m$]
=$4A_c/P$ [$m$]	=
$f$	=	friction factor of the air flow through the heat exchanger without wedge [-]
$f_w$	=	friction factor of the air flow through the heat exchanger with wedge [-]
$h_o$	=	the air side heat transfer coefficient [$W{m^{-2}}^{\circ }{C}^{-1}$]
${\bar{h}}_o$	=	the overall air side heat transfer coefficient of the heat exchanger [$W{m^{-2}}^{\circ }{C}^{-1}$]
$h_i$	=	the water side heat transfer coefficient [$W{m^{-2}}^{\circ }{C}^{-1}$]
$h_{\theta }$ local heat transfer coefficient [$W{m^{-2}}^{\circ }{C}^{-1}$]	=
$h_{o,w}$	=	the air side heat transfer coefficient of the heat exchanger with wedge [$W{m^{-2}}^{\circ }{C}^{-1}$]
${\bar{h}}_{o,w}$	=	the overall air side heat transfer coefficient of the heat exchanger with wedge [$W{m^{-2}}^{\circ }{C}^{-1}$]
$k$	=	thermal conductivity of the tube [$W{m^{-1}}^{\circ }{C}^{-1}$]
$l$	=	the distance between pressure traps [$m$]
$L$	=	the heat exchanger length [$m$]
$P$	=	the duct perimeter [$m$]
$\mathrm{\Delta }P$	=	pressure drop of air flow through the heat exchanger [$Pa$]
$Q{\hspace{0.17em}}_w$	=	water volumetric flow rate [$m^3\cdot s^{-1}$]
$r_i$	=	the inside radius of the tube [$m$]
$r_o$	=	the outside radius of the tube [$m$]
$S_L$	=	longitude tube pitch [$m$]
$S_T$	=	transverse tube pitch [$m$]
$T_{o,i}$	=	inlet air temperature [${ }^{\circ }C$]
$T_{a,o}$	=	outlet air temperature [${ }^{\circ }C$]
$T_{w,o}$	=	outlet water temperature [${ }^{\circ }C$]
$T_{w,i}$	=	inlet water temperature [${ }^{\circ }C$]
$\mathrm{\Delta }{T}_{ln}$	=	the logarithm mean temperature difference [${ }^{\circ }C$]
$TEF$	=	thermal efficiency factor [-]
$U$	=	overall heat transfer coefficient [$W{m^{-2}}^{\circ }{C}^{-1}$]
$v$	=	average free air velocity [$m{s}^{-1}$]
$x$	=	distance from the inlet of the tube bundle [$m$]
Greek symbols	=
$\alpha$	=	aspect ratio $=b/e$ [-]
$\mu$	=	kinematic viscosity [$Pa\cdot s$]
$\theta$	=	the angle from the front end[${ }^{\circ }$]
$\rho$	=	the air density [$kg\cdot m^{-3}$]
$\tau$	=	wall shear stress at the tube [$N\cdot m^{-2}$]
${\tau }_{\theta }$	=	local wall shear stress at the tube [$N\cdot m^{-2}$]
${\tau }_x$	=	local wall shear stress at the shell of the heat exchanger without wedge [$N\cdot m^{-2}$]
${\tau }_{x,w}$	=	local wall shear stress at the shell of the heat exchanger with wedge [$N\cdot m^{-2}$]
${\rho }_w$	=	the water density [$kg\cdot m^{-3}$]
$Re$	=	Reynolds number [-]
$Re=\frac{\rho v{D}_h}{\mu }$	=